Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$19.44	7.488%	$20.8957	$20.90	$20.90	$20.90
Purchase #2	$124.42	10.873%	$137.9482	$137.95	$137.95	$137.90
Purchase #3	$58.96	11.234%	$65.5836	$65.58	$65.60	$65.60
Purchase #4	$143.37	12.167%	$160.8138	$160.81	$160.80	$160.80
Purchase #5	$93.51	7.586%	$100.6037	$100.60	$100.60	$100.60
Purchase #6	$31.86	5.389%	$33.5769	$33.58	$33.60	$33.60
Purchase #7	$148.58	10.482%	$164.1542	$164.15	$164.15	$164.20
7 purchase totals =	$620.14		$683.5761	$683.57	$683.60	$683.60